The objectives of the Registry of Experimental Cancers are the storage and retrieval of pathological material and data on cancers and other lesions of laboratory animals (primarily rodents) and the use of such information for research and educational purposes. The Registry's designation as The World Health Organization Collaborating Centre for Reference on Tumours of Laboratory Animals was renewed for four years. During the current year the Registry has acquired 725 single or group accessions reaching a total of 13,383 (an accession usually corresponds to an animal autopsy). The number of diagnostic records added this year was 2606, bringing the total of records coded since the establishment of the Registry to 76,668 (a record usually corresponds to a diagnosis). During this year 48 investigators have come to the Registry for study and consultation on a single or multiple visits. A total of 191 study sets were loaned to investigators throughout the world. An extensive review on mouse pituitary tumors was completed by Dr. A.G. Liebelt, with inclusion of new histological materials and new documentation (photographs, tables). This review was used to update the relevant chapter in "Pathology of Tumours in Laboratory Animals, Vol. II-Tumours in the Mouse," to be published by the International Agency for Research on Cancer. A new activity was undertaken to provide search and retrieval capabilities to the Registry's computer database. In collaboration with the Division of Computer Research and Technology, NIH, and with the Department of Laboratory Services, Baltimore Veterans Administration Hospital, a pilot computer program was developed using a sample of 1000 entries from the Registry's database. Rapid and effective retrieval and indexing capabilities were obtained. The program is currently being further refined and extended.